1. Field of the Invention
The present invention relates to signal processing, and, in particular, to the encoding of video data, especially sequences of palettized video images.
2. Description of the Related Art
In some image and graphics processing environments, the colors available for representing video images are limited to those defined in a color lookup table (CLUT) of limited size. For example, an 8-bit CLUT provides up to 256 different colors, each of which is identified by a CLUT index. The color lookup table maps each index value to a corresponding color represented in a different format, for example, 24-bit three-component RGB format. Video sequences that are represented by CLUT indices are called palettized video sequences. A palettized video sequence may be compressed into an encoded bitstream for transmission and/or storage for real-time and/or future decoding. After the encoded bitstream is decompressed, the color lookup table may be used to convert the decoded palettized video data to three-component data for display.
Unlike three-component video data which can be encoded using lossy compression schemes and still achieve acceptable quality during playback of the decoded video images, it is often desirable to encode palettized video streams losslessly to maintain satisfactory decode quality. The present invention relates to the encoding and decoding of palettized video data using a lossless compression scheme.
Further objects and advantages of this invention will become apparent from the detailed description of a preferred embodiment which follows.